1. Field of the Invention
The present invention relates to a cable-type steering device for a vehicle in which a steering wheel and a steering gearbox are connected to each other by a flexible cable such as a Bowden cable.
2. Description of the Related Art
In the case of a conventional steering device for a vehicle, the bottom end of a steering shaft having a steering wheel at its top end is connected to a steering gearbox to transmit a steering torque input to the steering wheel to a rack-and-pinion mechanism set in the steering gearbox through the steering shaft.
However, when connecting the steering wheel with the steering gearbox by the steering shaft, certain design problems occur. For example, the degree of freedom for design is greatly limited. Moreover, the steering gearbox cannot be used commonly in a right-hand steered vehicle and a left-hand steered vehicle because it is difficult to freely select a position of the steering wheel relative to the steering gearbox. Moreover, because vibrations inputted to tires from the surface of a road and vibrations of an engine are inputted to the steering wheel through the steering shaft, comfort problems are experienced in that the silence within a vehicle compartment and the riding comfort of the vehicle deteriorate.
Therefore, a cable-type steering device has been proposed in Japanese Patent Application Laid-Open No. 8-2431) which uses a flexible transmission means such as a Bowden cable instead of a conventional steering shaft. With the proposed device it is possible to freely select a position of the steering wheel relative to the steering gearbox and the above comfort problems are minimized because road vibrations and vibrations of the steering gearbox are not readily transmitted to the steering wheel.
When combining a cable-type steering device with an electric power steering device, it is possible to assist the driver's steering by detecting a steering torque input to a steering wheel and driving an actuator of the electric power steering device in response to the steering torque so detected. To detect the steering torque in accordance with the tension of a cable, it is necessary to move a detection member of a tension detection means into contact with the cable. However, because the cable of a cable-type steering device is generally a stranded metal wire having a high strength, a problem occurs when the cable slides while contacting the detection member. That is, the detection member finely vibrates due to irregularity of the surface of the cable which varies and disrupts the accurate detection of the tension of the cable.